1. Field of the Invention
The invention relates to a positive-working light-sensitive mixture containing a resinous binder that is insoluble in water but soluble or at least swellable in aqueous-alkaline solutions, and, as a light-sensitive compound, an o-naphthoquinonediazide-sulfonic acid ester of a diacylhexahydroxydiphenylmethane. The mixture is useful for the production of light-sensitive materials, for example, planographic printing plates and photoresists.
2. Description of Related Art
Diacylhexahydroxydiphenylmethane which is completely esterified with 1,2-naphthoquinone-2-diazide-4-sulfonic acid or 1,2-naphthoquinone-2-diazide-5-sulfonic acid is known from EP-52,788 (which is equivalent to U.S. Pat. No. 4,407,926) as a light-sensitive compound. The printing plates produced with these compounds have a light sensitivity which is adequate in practice, and an improved resistance to alkaline developers and to those organic solvents which are normally used during the copying work and during the printing process on the printing presses.
A disadvantage of these compounds is that their solubility in organic solvents such as, for example, glycol monoethers such as glycol monomethyl, monoethyl or monopropyl ether; carboxylic acid esters such as ethylacetate or butylacetate, ketones such as methyl ethyl ketone, cyclopentanone or cyclohexanone; and also aromatic hydrocarbons such as toluene or xylene, used for coating metal bases or plastic bases, is inadequate for some purposes. A further disadvantage is that resist layers containing these compounds as light-sensitive components, can, in the exposed state, be rapidly developed only with relatively strong aqueous-alkaline solutions. Such resist layers cannot be developed at an adequate speed, appropriate in practice, with the aqueous, weakly alkaline developers which are presently increasingly preferred for ecological reasons.
DE-C 938,233 (equivalent to GB-A 739,654) and U.S. Pat. No. 3,802,885, describe di- or trihydroxybenzophenones partially or completely esterified with o-naphthoquinonediazide-sulfonic acids as light sensitive compounds. These compounds readily dissolve in the conventional solvents used for coating metallic or non-metallic base materials and show a relatively high light sensitivity. Exposed resist layers of these compounds together with binders soluble in aqueous-alkaline media, for example, novolaks, can also be developed with aqueous, weakly alkaline solutions. As a rule, however, the resist layers show an inadequate developer resistance of the unexposed layer constituents. In addition, these layers are attacked to a greater or lesser extent during the printing process if alcohol-containing fountain solutions are used. The alcohol resistance of such layers is therefore in many cases inadequate for use in practice.
Further esters of o-naphthoquinonediazide-sulfonic acids and aromatic polyhydroxy compounds are known from DEC 1,118,606 (equivalent to GB-A 935,250). Inter alia, derivatives of diphenylmethane are also mentioned as phenolic components. The polyhydroxydiphenylmethane derivatives are, however, not completely esterified, so that they still contain at least one free hydroxyl group. Compounds of this type are not sufficiently soluble for some purposes in the solvents conventional for coating base materials. Their light sensitivity is generally adequate for use in practice, but the alcohol resistance of the light-sensitive resist layers produced with such compounds is not. Industrial use of these compounds is therefore possible only with severe restrictions.
EP-A 0,440,238 describes a photoresist mixture which, in addition to a polymer soluble in aqueous-alkaline solutions, contains aromatic polyhydroxy compounds which are partially esterified with 1,2-naphthoquinone-2-diazide-4-sulfonic or -5-sulfonic acid. The mixture can also contain up to 30% by weight of completely esterified polyhydroxy compounds. The aromatic polyhydroxy compounds are accessible only via a complicated reaction sequence. In contrast, the phenolic base compounds previously described, which form the starting point of the present invention, are already known and are easily accessible.